Merge pull request #922 from asbjornu/feature/os-x-build

Instruct Travis to build on OS X

Author: pascalberger

.travis.yml

@@ -1,6 +1,11 @@
 language: csharp
 solution: src/GitVersion.sln
 sudo: false
+mono:
+  - latest
+os:
+  - linux
+  - osx
 before_install: # We need to download nuget.exe due to: https://github.com/travis-ci/travis-ci/issues/5932
   - mkdir -p .nuget
   - wget -O .nuget/nuget.exe https://dist.nuget.org/win-x86-commandline/latest/nuget.exe